Nosing around filter... is this a problem?

[CharminglyOdd]

We have a filter that stands upright in the tank. I keep hearing, on and off, a gulping noise but when I've looked the two goldfish have been nowhere near the surface. Just happened to look up as it happened and the larger one is nosing around the flat top of the filter, where the bubbles come out, and is trying to nibble the top of it causing the gulping noise.

I suspect the 'gulp' (sounds like a large drop of water hitting the surface) is probably not very healthy or is it okay for him to be doing this - is there a risk of an air bubble inside him if he swallows air?

If it's not good for him is there anything I can do to mitigate it please? They are due a thorough clean at the weekend so could put something in place then to minimise disturbance. They are very active and seem happy little souls - don't look distressed or sick.

If they are gasping at the surface then it might be a sign of low oxygen levels in the water, or possibly that they are having trouble absorbing oxygen (this can be due to gill damage or nitrIte poisoning). How big is the tank? Do you have recent water test results?

Sorry, maybe I wasn't clear - it's not the surface but the top of the filter (two or three inches below the surface - I can see I missed that bit out :) ) where the bubbles come out. I'm concerned they might be swallowing the bubbles inadvertently (gulping noise, can't think that just nosing around the bubbles without swallowing would make that noise).

Is it normal for them to nose around and should I be putting something (maybe a fine mesh?) over the top of the filter to stop them swallowing bubbles please? Or have I got fish anatomy wrong (very likely!) and it's impossible for them to swallow the bubbles?

It's only the one fish that's doing this, having seen him do it as I was typing. He's grown to twice the size of the other and is a lionhead but without the pronounced arched spine I see when I google <a class="break-all" href="http://www.google.co.uk/imgres?q=lionhead+goldfish&hl=en&safe=off&sa=X&rlz=1C1ASUT_en-GBGB434GB434&biw=1366&bih=667&tbm=isch&prmd=imvns&tbnid=Dz2i0-0tlmDXoM:&imgrefurl=animal-world.com/encyclo/fresh/goldfish/LionheadGoldfish.php&docid=-uCyYJ5iCfTeFM&imgurl=animal-world.com/encyclo/fresh/goldfish/images/lionhead.jpg&w=258&h=176&ei=F9ZDT4jOG8LO0QXfveGPDw&zoom=1&iact=hc&vpx=930&vpy=182&dur=1756&hovh=140&hovw=206&tx=94&ty=107&sig=105921918342724744766&page=1&tbnh=140&tbnw=176&start=0&ndsp=18&ved=0CFMQrQMwBA" rel="nofollow" target="_blank">very similar to the one here with the blue background. The other is a normal fantail goldfish.

Also, just as an aside... can they see out of the tank? We've had them just over a year now and as time has gone on they have become more and more friendly (for want of a better word!). If they can't feel vibration/there's no light source then they either float or swim around at the back/away from people but if you move near them for any period of time they come over and start nosing against the edge of the tank to say hello.

Are they really doing it as I've described please or are we one of those mad couples who imprints human-like behaviour onto their pets?

Yes, they can see out of the tank. Fish have pretty good eyesight (some breeds of goldfish with funny shaped eyes can't see as well) and I think there was an experiment once that showed that they can tell people apart and will put on more of a show for the person who is most likely to feed them

The bit where the bubbles come out of the filter would be the part of the tank with the highest oxygen level so if it's going on a lot then there still could be cause for concern. How big is the tank? Is the filter outlet disturbing the surface of the water?

It does disturb the surface of the water. The 'tank' is a large fish bowl sold to us when we were young and stupid didn't know much about fish. I do need to get them a larger tank and cycle it through but that won't be happening until I get a job as DP doesn't see the problem with things as they are

TBH I know the tank is the biggest problem and it is getting worse now they are growing up. I have read posts about getting tanks on freecycle but, having had our fingers burned with bad advice from the fish shop on several occasions, I don't want to trust someone else WRT the quality of an old tank and would rather buy a new one. If that's the area with the most oxygen then that seems to be another tank-size related issue.

They definitely fuss DP more (he feeds them, it's his one fish-related job ) but they will come and chat to me as well. It's very cute.

Thank you very much for your help :)

There are a lot of good quality second hand tanks around due to people buying brand new, being given crap advice and so selling it all when its only a few months old. It's worth having a look, goldfish need a pretty big tank so if you're on a budget you could save money on the tank and use it to get a decent external filter.

Here are some guidelines about how much space they need.